Micafungin is a second clinically applied pneumocandins drug after caspofungin. It mostly inhibits the synthesis of the main ingredient of fungi cell walls, i.e. 1,3-β-D-dextran, and therefore disrupts the formation of fungi cell walls and influences cell morphology and osmotic pressure thereof, thus leading to cytolysis and cell death. Micafungin is mainly used for treating deep fungi infections such as that from Monilia, Aspergillus, etc. In particular, it is used for treating fungi infections in patients with low immunity, such as chemotherapy patients, AIDS patients, etc. Clinically, it is also used in combination with amphotericin and triazole anti-fungi drugs.
Micafungin is developed by Fujisawa Pharmaceutical, under the trade name of Mycamine. Micafungin is on the market as sodium form, the formula of which is shown as follows.

WO9611210 and WO2004014879 have reported processes for synthesis and purification of micafungin.
WO9611210 has reported a method for obtaining the sodium salt by using cation exchange resin (DOWEX-50WX4). It is impossible to control the pH value of the product using said method. In addition, this method only applies to small-scale preparation. It is hardly suited for expanded scale of production and quality of products thereof is unmanageable.
WO2004014879 has reported a method using 0.1 mol/L NaOH solution to adjust pH value to 6-8. The Inventors have performed multiple experiments using methods reported in the literature and have discovered that adjusting the pH value according to said method leads to a significant rise in the content of impurity from micafungin degradation, as is shown in FIGS. 2 and 3, thereby considerably increasing the difficulty in the subsequent separation and purification and it is difficult to prepare micafungin sodium of high purity. Hence, the method can not fulfil the requirements for industrialized manufacture.
Therefore, it is urgent to develop a method for the preparation of micafungin sodium in order to obtain micafungin sodium of high purity.